In the glass molding industry, and particularly in the operation of plural mold machines for the manufacture of bottles or the like, the cooling of the molds is critical in terms of mold life, quality of molded product and speed of operation of the molding machine. The faster the operation of the machine, the greater number of units manufactured per unit time and the greater the amount of heat added to the molds per unit time becomes. It has been apparent therefore, that in order to speed up the operation of a machine of this type, the excess mold heat must be uniformly removed and at a correspondingly faster rate of heat transfer. In the past, air cooled molding arrangements have been employed, but these are inefficient and may require electrically driven fans with motor ratings of the order of 250 horsepower. To effect a more efficient cooling process, the use of liquid rather than air cooling was proposed, but not only was this difficult to control, but in most cases, it resulted in too rapid a chilling of the mold with a consequent decrease in quality of the molded product. In my aforementioned co-pending application, I have suggested a cooling process wherein each mold is formed with a plurality of blind axially extending bores between the mold surface and the mold exterior, and these bores are at least partially filled with a phase change liquid such, for example, as distilled water. By connecting the upper ends of these blind bores to a common manifold and arranging a condenser vertically above that manifold and connecting the two with a vertically extending closed conduit, I have shown that it is possible to increase the efficiency of mold cooling by causing the heat from the molding material to be transferred from the mold proper to the phase change liquid causing it to vaporize, move upwardly through the common manifold to the condenser and then fall back by gravity to the individual blind bores from which it originated.
I have since discovered that the most efficient cooling is when the heat of the mold is transferred not to a liquid, but to a vapor which is in contact with the walls of the plurality of blind bores.
Particularly in the case of multiple cavity molds, it is advantageous to utilize a separate common manifold for the blind bores in each mold half. Taking as an example a three cavity mold, the center cavity has less exposed surfaces than the outer two and therefor requires more cooling. By using a separate manifold for each mold half, it is possible to provide and control different cooling rates for individual mold cavities and thereby insure uniform quality of all articles formed in multiple cavity molds.
With the apparatus of this invention, it becomes possible to achieve a mold cooling rate which is inversely proportional to the flow rate of secondary coolant through the condenser.